How Cows Make Milk

Reader Contribution by Steve Judge and Bob-White Systems
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Properly fed cows enjoy diets rich in hay and grass. Both are rich in cellulose. This alone is remarkable because cellulose is very difficult to digest. Humans lack the ability to digest cellulose but the digestive systems of cows have evolved specifically to digest it. A diet that includes plenty of grass and long-stemmed hay is critical for keeping cows healthy so they can enjoy good, long lives. We graze our cows on wooded pastures, for example.

The Four Cow Stomachs

Cows are ruminants, which means they have four stomachs or four stomach compartments. Other ruminants include goats, sheep, water buffalo, etc. Each one of the four stomachs plays a different role in digesting food and making milk. 

The rumen is the cow’s first stomach, where the partly chewed grass initially enters. Upon arrival, it is mixed with water and partially broken down by stomach juices and microbes. The rumen can hold over 25 gallons of the mixture.

The grass then passes into the reticulum where it is further softened and made into small wads called cuds. The cuds return to the cow’s mouth one by one where they are chewed 40 to 60 times, which takes about one minute per cud. Cows enjoy chewing their cud and seem to get lost in peaceful thought while doing it.

The chewed cud goes to the omasum where it is pressed by to remove much of the water and is further digested. 

The cud then passes into the abomasum where the digestion process is completed. The digested milk then enters the cow’s small intestine where the nutrients contained in the grass and hay are absorbed by the cow. The abomasum can sometimes cause problems for both the cow and farmer. It can fill with gas and actually float out of position in the cow’s body and become twisted and blocked. The condition is called a Displace Abomasum or DA and is fairly common.

When this happens, a cow will stop eating and become lethargic. If not treated soon, her health will go down hill quickly. Usually the condition can be corrected surgically. Sometimes it can be corrected, at least temporarily, by rolling the cow.

Though a DA usually occurs shortly after a cow calves, due to the shifting of the cows internal organs, after the calf is born, I have found that DAs can be reduced, if not prevented, by a diet rich in grass and long-stemmed hay.

The Udder

Once the grass, hay and other nutrients have been absorbed into the cow’s bloodstream, they are delivered to the cow’s udder where more magic happens. A cow’s udder has four quarters or compartments. Each quarter has its own teat or nipple where the calf nurses and the milk exits. Inside, each quarter is full of mammary glands, called “alveoli,” and a milk cistern where the milk drains before it enters the teat cistern. Every good farmer has a reliable teat dip on hand — we offer a package that has all the essentials here.

The alveoli are tiny balloon-like milk making machines that are fueled by nutrients carried to them by the cow’s blood stream. Cells lining the alveoli produce milk, which is then released into the interior cavity of each alveolus called the Alveolus Lumen.

When the udder is stimulated by a nursing calf or by being prepped for milking by the farmer, the cow releases oxytocin into her blood stream, which causes the alveolus to contract and release the milk, which then travels down to the milk cistern and teat. The process is called “letting down.” If it’s your first time milking a cow, you may want to read our How to Milk a Cow blog ahead of time.

Sometimes, first calf heifers (young cows) being milked for the first few times will have problems letting down. Frightened or injured cows may have problems letting down as well. Usually those cows eventually relax and milk out just fine. However, in some stubborn cases the farmer may decide to give the cow a small injection of oxytocin. Doing so on a regular basis should be avoided, because a cow can become “addicted” to the injection. Massaging the udder can be an excellent alternative.

For more tips and tricks on the proper handling of a cow, read on.

Managing Cow Udders

The conformation of a cow’s udder can make or break the cow. Some cows can produce 100 pounds or more of milk every day. If they are milked twice a day the udder may contain 50 pounds of milk or more when she is milked. That is a lot of weight. A cow’s udder is held in place by suspensory and lateral ligaments. If those ligaments are weak or fail, the udder can hang too low where it can be injured or pick up bacterial infections called “mastitis.”

We have a blog post on how to keep your dairy animals clean when milking, that’s proven to be very helpful for fellow farmers. Also, milking a cow with a big udder hanging low can be difficult and unpleasant and can end a cow’s career. Ideally, a cow’s udder should be tucked up nicely between her rear legs and her teats should not extend below her hock joints. Remember to have your livestock care and supplies ready to go before starting this process.

In my next posts, I will discuss the various ways cows are milked on small herd dairies. I will start with The Basics of Milking Cows.

Steve Judge is a long-time dairy farmer and micro-dairy expert at Bob-White Systems. Driven by a passion for the Slow Food movement and a desire for communities to enjoy locally produced, Steve’s goal is to create appropriately scaled dairy technology and equipment that will give small-scale dairy farmers the opportunity to sell safe, farm fresh milk and dairy products directly from their farms to friends and neighbors. Read all of Steve’s MOTHER EARTH NEWS posts here

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